When an electronic component such as a flip chip is mounted on a circuit member such as a printed substrate, a reflow method is widely used, the method including the steps of: interposing solder and a bonding material including a thermosetting resin between an electrode on the component and an electrode on the substrate; and then heating the solder and the bonding material to cause the solder to melt and the thermosetting resin to cure. The molten solder spreads between the electrodes and wets them; and is then cooled to form a solder joint therebetween. Thus, an electrical connection is achieved between the electrodes. Meanwhile, the cured substance of the thermosetting resin becomes a resin-reinforced portion for protecting the solder joint.
As one mounting method by the reflow method, a proposal has been made to use a thermosetting resin which cures at a temperature lower than the melting point of the solder, by first causing the resin to cure at a low temperature and then heating the solder at a temperature equal to or higher than its melting point, thereby to bond the electrodes together via the solder (c.f., Patent Literature 1). In this mounting method, curing of the thermosetting resin and melting of the solder are conducted while the electronic component is pressed against the circuit member. This is because the distance between the electrode on the circuit member and the electrode on the electronic component usually varies. Moreover, this is to prevent poor electric connection due to the interposition of the thermosetting resin between the electrodes as well as poor contact between the molten solder and the electrodes.
There has also been a proposal to pre-coat an electrode on a circuit member with solder in advance, and to then mount an electronic component with solder bumps on the circuit member via a thermosetting resin. At the time of mounting, the lower end portion of the solder bumps is made to wedge into the pre-coat solder. In this case, a proposal has been made to cause curing of the thermosetting resin and melting of the solder without any pressing of the electronic component against the circuit member (c.f., Patent Literature 2).